drivers/gpio: added GPIO_UNDEF define
drivers/gpio: added GPIO_UNDEF define

wentaoshang/RIOT,kYc0o/RIOT,LudwigKnuepfer/RIOT,msolters/RIOT,rfuentess/RIOT,ks156/RIOT,robixnai/RIOT,Hyungsin/RIOT-OS,authmillenon/RIOT,automote/RIOT,arvindpdmn/RIOT,Hyungsin/RIOT-OS,PSHIVANI/Riot-Code,RubikonAlpha/RIOT,lazytech-org/RIOT,stevenj/RIOT,miri64/RIOT,rakendrathapa/RIOT,ThanhVic/RIOT,Osblouf/RIOT,x3ro/RIOT,A-Paul/RIOT,kushalsingh007/RIOT,sumanpanchal/RIOT,gbarnett/RIOT,jbeyerstedt/RIOT-OTA-update,msolters/RIOT,jremmert-phytec-iot/RIOT,mtausig/RIOT,neiljay/RIOT,jremmert-phytec-iot/RIOT,MonsterCode8000/RIOT,centurysys/RIOT,ntrtrung/RIOT,RBartz/RIOT,mfrey/RIOT,brettswann/RIOT,alex1818/RIOT,luciotorre/RIOT,automote/RIOT,kerneltask/RIOT,mziegert/RIOT,biboc/RIOT,adjih/RIOT,rfswarm/RIOT,mfrey/RIOT,latsku/RIOT,RIOT-OS/RIOT,Osblouf/RIOT,tdautc19841202/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,jfischer-phytec-iot/RIOT,latsku/RIOT,RubikonAlpha/RIOT,haoyangyu/RIOT,binarylemon/RIOT,adrianghc/RIOT,abp719/RIOT,cladmi/RIOT,wentaoshang/RIOT,haoyangyu/RIOT,jremmert-phytec-iot/RIOT,DipSwitch/RIOT,jfischer-phytec-iot/RIOT,alignan/RIOT,openkosmosorg/RIOT,plushvoxel/RIOT,MonsterCode8000/RIOT,stevenj/RIOT,lazytech-org/RIOT,TobiasFredersdorf/RIOT,khhhh/RIOT,syin2/RIOT,thomaseichinger/RIOT,Osblouf/RIOT,malosek/RIOT,mziegert/RIOT,brettswann/RIOT,phiros/RIOT,rousselk/RIOT,kaleb-himes/RIOT,kb2ma/RIOT,shady33/RIOT,MarkXYang/RIOT,neiljay/RIOT,authmillenon/RIOT,marcosalm/RIOT,alex1818/RIOT,kbumsik/RIOT,Josar/RIOT,luciotorre/RIOT,OlegHahm/RIOT,yogo1212/RIOT,LudwigKnuepfer/RIOT,herrfz/RIOT,shady33/RIOT,kerneltask/RIOT,asanka-code/RIOT,altairpearl/RIOT,FrancescoErmini/RIOT,JensErdmann/RIOT,jferreir/RIOT,marcosalm/RIOT,basilfx/RIOT,ximus/RIOT,smlng/RIOT,basilfx/RIOT,l3nko/RIOT,kYc0o/RIOT,beurdouche/RIOT,changbiao/RIOT,lebrush/RIOT,Lexandro92/RIOT-CoAP,authmillenon/RIOT,latsku/RIOT,robixnai/RIOT,aeneby/RIOT,kb2ma/RIOT,thomaseichinger/RIOT,mtausig/RIOT,x3ro/RIOT,mziegert/RIOT,cladmi/RIOT,kbumsik/RIOT,altairpearl/RIOT,dailab/RIOT,LudwigOrtmann/RIOT,sumanpanchal/RIOT,jbeyerstedt/RIOT-OTA-update,ntrtrung/RIOT,roberthartung/RIOT,tdautc19841202/RIOT,dkm/RIOT,shady33/RIOT,biboc/RIOT,msolters/RIOT,basilfx/RIOT,arvindpdmn/RIOT,syin2/RIOT,smlng/RIOT,jferreir/RIOT,plushvoxel/RIOT,koenning/RIOT,EmuxEvans/RIOT,gbarnett/RIOT,jfischer-phytec-iot/RIOT,gautric/RIOT,khhhh/RIOT,BytesGalore/RIOT,Osblouf/RIOT,Yonezawa-T2/RIOT,jremmert-phytec-iot/RIOT,Yonezawa-T2/RIOT,tfar/RIOT,phiros/RIOT,josephnoir/RIOT,neiljay/RIOT,toonst/RIOT,binarylemon/RIOT,ThanhVic/RIOT,alignan/RIOT,MonsterCode8000/RIOT,jfischer-phytec-iot/RIOT,backenklee/RIOT,rfuentess/RIOT,tdautc19841202/RIOT,automote/RIOT,phiros/RIOT,DipSwitch/RIOT,kYc0o/RIOT,binarylemon/RIOT,hamilton-mote/RIOT-OS,rfuentess/RIOT,rakendrathapa/RIOT,rfswarm/RIOT,sumanpanchal/RIOT,TobiasFredersdorf/RIOT,abp719/RIOT,roberthartung/RIOT,jasonatran/RIOT,ximus/RIOT,EmuxEvans/RIOT,thiagohd/RIOT,Yonezawa-T2/RIOT,RBartz/RIOT,herrfz/RIOT,dailab/RIOT,wentaoshang/RIOT,gbarnett/RIOT,gbarnett/RIOT,rajma996/RIOT,OlegHahm/RIOT,yogo1212/RIOT,binarylemon/RIOT,adjih/RIOT,mziegert/RIOT,neumodisch/RIOT,PSHIVANI/Riot-Code,sumanpanchal/RIOT,kerneltask/RIOT,kushalsingh007/RIOT,Osblouf/RIOT,wentaoshang/RIOT,LudwigKnuepfer/RIOT,dhruvvyas90/RIOT,JensErdmann/RIOT,d00616/RIOT,bartfaizoltan/RIOT,neumodisch/RIOT,chris-wood/RIOT,aeneby/RIOT,kaleb-himes/RIOT,josephnoir/RIOT,marcosalm/RIOT,BytesGalore/RIOT,cladmi/RIOT,kushalsingh007/RIOT,Darredevil/RIOT,openkosmosorg/RIOT,attdona/RIOT,kbumsik/RIOT,Josar/RIOT,openkosmosorg/RIOT,kaleb-himes/RIOT,Josar/RIOT,immesys/RiSyn,DipSwitch/RIOT,OTAkeys/RIOT,MohmadAyman/RIOT,gbarnett/RIOT,thiagohd/RIOT,zhuoshuguo/RIOT,rakendrathapa/RIOT,smlng/RIOT,neiljay/RIOT,rfswarm/RIOT,openkosmosorg/RIOT,ant9000/RIOT,hamilton-mote/RIOT-OS,FrancescoErmini/RIOT,alignan/RIOT,FrancescoErmini/RIOT,lebrush/RIOT,MarkXYang/RIOT,ks156/RIOT,l3nko/RIOT,yogo1212/RIOT,phiros/RIOT,tfar/RIOT,plushvoxel/RIOT,OTAkeys/RIOT,ntrtrung/RIOT,asanka-code/RIOT,MarkXYang/RIOT,Darredevil/RIOT,dhruvvyas90/RIOT,brettswann/RIOT,kb2ma/RIOT,binarylemon/RIOT,LudwigOrtmann/RIOT,RubikonAlpha/RIOT,TobiasFredersdorf/RIOT,koenning/RIOT,Yonezawa-T2/RIOT,LudwigOrtmann/RIOT,dailab/RIOT,katezilla/RIOT,kaspar030/RIOT,rajma996/RIOT,zhuoshuguo/RIOT,zhuoshuguo/RIOT,RIOT-OS/RIOT,immesys/RiSyn,mtausig/RIOT,RIOT-OS/RIOT,luciotorre/RIOT,x3ro/RIOT,dkm/RIOT,abkam07/RIOT,jasonatran/RIOT,benoit-canet/RIOT,rousselk/RIOT,chris-wood/RIOT,l3nko/RIOT,EmuxEvans/RIOT,lebrush/RIOT,brettswann/RIOT,thiagohd/RIOT,MohmadAyman/RIOT,miri64/RIOT,LudwigKnuepfer/RIOT,abkam07/RIOT,changbiao/RIOT,Darredevil/RIOT,A-Paul/RIOT,wentaoshang/RIOT,avmelnikoff/RIOT,alignan/RIOT,shady33/RIOT,adrianghc/RIOT,ant9000/RIOT,toonst/RIOT,FrancescoErmini/RIOT,attdona/RIOT,LudwigKnuepfer/RIOT,RBartz/RIOT,gebart/RIOT,OlegHahm/RIOT,changbiao/RIOT,mziegert/RIOT,arvindpdmn/RIOT,OTAkeys/RIOT,josephnoir/RIOT,alex1818/RIOT,wentaoshang/RIOT,MonsterCode8000/RIOT,syin2/RIOT,aeneby/RIOT,toonst/RIOT,neumodisch/RIOT,A-Paul/RIOT,Lexandro92/RIOT-CoAP,thomaseichinger/RIOT,jferreir/RIOT,dkm/RIOT,alex1818/RIOT,bartfaizoltan/RIOT,stevenj/RIOT,Ell-i/RIOT,Hyungsin/RIOT-OS,josephnoir/RIOT,RubikonAlpha/RIOT,syin2/RIOT,backenklee/RIOT,neumodisch/RIOT,herrfz/RIOT,d00616/RIOT,ks156/RIOT,Darredevil/RIOT,l3nko/RIOT,benoit-canet/RIOT,tfar/RIOT,gebart/RIOT,backenklee/RIOT,phiros/RIOT,plushvoxel/RIOT,stevenj/RIOT,JensErdmann/RIOT,asanka-code/RIOT,rfuentess/RIOT,patkan/RIOT,stevenj/RIOT,kushalsingh007/RIOT,centurysys/RIOT,beurdouche/RIOT,immesys/RiSyn,brettswann/RIOT,miri64/RIOT,BytesGalore/RIOT,alex1818/RIOT,arvindpdmn/RIOT,adjih/RIOT,JensErdmann/RIOT,asanka-code/RIOT,adjih/RIOT,RBartz/RIOT,koenning/RIOT,haoyangyu/RIOT,ximus/RIOT,jfischer-phytec-iot/RIOT,kYc0o/RIOT,patkan/RIOT,cladmi/RIOT,MarkXYang/RIOT,katezilla/RIOT,rakendrathapa/RIOT,Ell-i/RIOT,basilfx/RIOT,gautric/RIOT,neumodisch/RIOT,ntrtrung/RIOT,rfswarm/RIOT,kerneltask/RIOT,haoyangyu/RIOT,MonsterCode8000/RIOT,smlng/RIOT,lazytech-org/RIOT,chris-wood/RIOT,dhruvvyas90/RIOT,rajma996/RIOT,RubikonAlpha/RIOT,roberthartung/RIOT,PSHIVANI/Riot-Code,kbumsik/RIOT,robixnai/RIOT,zhuoshuguo/RIOT,DipSwitch/RIOT,benoit-canet/RIOT,robixnai/RIOT,patkan/RIOT,malosek/RIOT,mfrey/RIOT,l3nko/RIOT,khhhh/RIOT,tfar/RIOT,katezilla/RIOT,kaleb-himes/RIOT,gautric/RIOT,Hyungsin/RIOT-OS,hamilton-mote/RIOT-OS,attdona/RIOT,jasonatran/RIOT,ks156/RIOT,d00616/RIOT,dkm/RIOT,abkam07/RIOT,TobiasFredersdorf/RIOT,l3nko/RIOT,RubikonAlpha/RIOT,BytesGalore/RIOT,ntrtrung/RIOT,patkan/RIOT,thiagohd/RIOT,dhruvvyas90/RIOT,RBartz/RIOT,EmuxEvans/RIOT,RIOT-OS/RIOT,centurysys/RIOT,ThanhVic/RIOT,yogo1212/RIOT,chris-wood/RIOT,toonst/RIOT,watr-li/RIOT,gebart/RIOT,asanka-code/RIOT,beurdouche/RIOT,kYc0o/RIOT,centurysys/RIOT,altairpearl/RIOT,backenklee/RIOT,ant9000/RIOT,daniel-k/RIOT,lebrush/RIOT,smlng/RIOT,LudwigOrtmann/RIOT,altairpearl/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,marcosalm/RIOT,Darredevil/RIOT,haoyangyu/RIOT,lebrush/RIOT,khhhh/RIOT,authmillenon/RIOT,biboc/RIOT,jferreir/RIOT,latsku/RIOT,tdautc19841202/RIOT,msolters/RIOT,immesys/RiSyn,gebart/RIOT,herrfz/RIOT,jbeyerstedt/RIOT-OTA-update,tdautc19841202/RIOT,dhruvvyas90/RIOT,MonsterCode8000/RIOT,PSHIVANI/Riot-Code,d00616/RIOT,aeneby/RIOT,ks156/RIOT,PSHIVANI/Riot-Code,abp719/RIOT,watr-li/RIOT,rfuentess/RIOT,rousselk/RIOT,jasonatran/RIOT,gautric/RIOT,tfar/RIOT,rajma996/RIOT,rfswarm/RIOT,koenning/RIOT,OlegHahm/RIOT,asanka-code/RIOT,neiljay/RIOT,benoit-canet/RIOT,ThanhVic/RIOT,MarkXYang/RIOT,abp719/RIOT,A-Paul/RIOT,jasonatran/RIOT,dkm/RIOT,adrianghc/RIOT,sumanpanchal/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,JensErdmann/RIOT,attdona/RIOT,bartfaizoltan/RIOT,jremmert-phytec-iot/RIOT,kb2ma/RIOT,ntrtrung/RIOT,rfswarm/RIOT,ximus/RIOT,khhhh/RIOT,malosek/RIOT,watr-li/RIOT,thiagohd/RIOT,koenning/RIOT,PSHIVANI/Riot-Code,watr-li/RIOT,dailab/RIOT,zhuoshuguo/RIOT,yogo1212/RIOT,lebrush/RIOT,Josar/RIOT,arvindpdmn/RIOT,automote/RIOT,malosek/RIOT,kaspar030/RIOT,daniel-k/RIOT,latsku/RIOT,katezilla/RIOT,changbiao/RIOT,JensErdmann/RIOT,ThanhVic/RIOT,beurdouche/RIOT,MohmadAyman/RIOT,luciotorre/RIOT,adrianghc/RIOT,attdona/RIOT,toonst/RIOT,cladmi/RIOT,biboc/RIOT,FrancescoErmini/RIOT,herrfz/RIOT,Lexandro92/RIOT-CoAP,jbeyerstedt/RIOT-OTA-update,x3ro/RIOT,biboc/RIOT,luciotorre/RIOT,marcosalm/RIOT,hamilton-mote/RIOT-OS,kushalsingh007/RIOT,MohmadAyman/RIOT,TobiasFredersdorf/RIOT,kaleb-himes/RIOT,adjih/RIOT,jferreir/RIOT,bartfaizoltan/RIOT,msolters/RIOT,Lexandro92/RIOT-CoAP,roberthartung/RIOT,watr-li/RIOT,aeneby/RIOT,chris-wood/RIOT,jbeyerstedt/RIOT-OTA-update,LudwigOrtmann/RIOT,benoit-canet/RIOT,miri64/RIOT,Ell-i/RIOT,thiagohd/RIOT,BytesGalore/RIOT,d00616/RIOT,A-Paul/RIOT,kerneltask/RIOT,kaspar030/RIOT,luciotorre/RIOT,d00616/RIOT,rousselk/RIOT,shady33/RIOT,lazytech-org/RIOT,adrianghc/RIOT,centurysys/RIOT,automote/RIOT,OlegHahm/RIOT,EmuxEvans/RIOT,abkam07/RIOT,Lexandro92/RIOT-CoAP,latsku/RIOT,Yonezawa-T2/RIOT,DipSwitch/RIOT,koenning/RIOT,gebart/RIOT,watr-li/RIOT,miri64/RIOT,Lexandro92/RIOT-CoAP,abkam07/RIOT,mtausig/RIOT,hamilton-mote/RIOT-OS,Ell-i/RIOT,backenklee/RIOT,Ell-i/RIOT,alex1818/RIOT,authmillenon/RIOT,mfrey/RIOT,daniel-k/RIOT,jferreir/RIOT,daniel-k/RIOT,rajma996/RIOT,ant9000/RIOT,josephnoir/RIOT,malosek/RIOT,katezilla/RIOT,alignan/RIOT,RBartz/RIOT,changbiao/RIOT,malosek/RIOT,arvindpdmn/RIOT,Osblouf/RIOT,mziegert/RIOT,ximus/RIOT,changbiao/RIOT,bartfaizoltan/RIOT,gautric/RIOT,automote/RIOT,daniel-k/RIOT,sumanpanchal/RIOT,patkan/RIOT,MohmadAyman/RIOT,abp719/RIOT,brettswann/RIOT,avmelnikoff/RIOT,rakendrathapa/RIOT,Hyungsin/RIOT-OS,ThanhVic/RIOT,MarkXYang/RIOT,thomaseichinger/RIOT,rousselk/RIOT,centurysys/RIOT,robixnai/RIOT,ant9000/RIOT,zhuoshuguo/RIOT,kaspar030/RIOT,LudwigOrtmann/RIOT,roberthartung/RIOT,thomaseichinger/RIOT,openkosmosorg/RIOT,stevenj/RIOT,binarylemon/RIOT,immesys/RiSyn,altairpearl/RIOT,openkosmosorg/RIOT,haoyangyu/RIOT,marcosalm/RIOT,mtausig/RIOT,avmelnikoff/RIOT,gbarnett/RIOT,altairpearl/RIOT,kaspar030/RIOT,mfrey/RIOT,Darredevil/RIOT,avmelnikoff/RIOT,herrfz/RIOT,yogo1212/RIOT,kbumsik/RIOT,Yonezawa-T2/RIOT,chris-wood/RIOT,RIOT-OS/RIOT,DipSwitch/RIOT,FrancescoErmini/RIOT,OTAkeys/RIOT,kb2ma/RIOT,OTAkeys/RIOT,abp719/RIOT,khhhh/RIOT,patkan/RIOT,daniel-k/RIOT,abkam07/RIOT,EmuxEvans/RIOT,basilfx/RIOT,MohmadAyman/RIOT,dhruvvyas90/RIOT,bartfaizoltan/RIOT,rousselk/RIOT,benoit-canet/RIOT,rakendrathapa/RIOT,beurdouche/RIOT,syin2/RIOT,tdautc19841202/RIOT,x3ro/RIOT,ximus/RIOT,attdona/RIOT,plushvoxel/RIOT,shady33/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,dailab/RIOT,msolters/RIOT,robixnai/RIOT,avmelnikoff/RIOT,immesys/RiSyn,neumodisch/RIOT,jremmert-phytec-iot/RIOT,authmillenon/RIOT,rajma996/RIOT,Josar/RIOT,phiros/RIOT,kushalsingh007/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,lazytech-org/RIOT